Finished drinking water usually contains some residual aluminum.The deposition of residual aluminum in distribution systems and potential release back to the drinking water could significantly influence the water quality at consumer taps.A preliminary analysis of aluminum content in cast iron pipe corrosion scales and loose deposits demonstrated that aluminum deposition on distribution pipe surfaces could be excessive for water treated by aluminum coagulants including polyaluminum chloride(PACl).In this work,the deposition features of different aluminum species in PACl were investigated by simulated coil-pipe test,batch reactor test and quartz crystal microbalance with dissipation monitoring.The deposition amount of non-polymeric aluminum species was the least,and its deposition layer was soft and hydrated,which indicated the possible formation of amorphous Al(OH)_3.Al_(13) had the highest deposition tendency,and the deposition layer was rigid and much less hydrated,which indicated that the deposited aluminum might possess regular structure and self-aggregation of Al_(13)could be the main deposition mechanism.While for Al_(30),its deposition was relatively slower and deposited aluminum amount was relatively less compared with Al_(13).However,the total deposited mass of Al_(30) was much higher than that of Al_(13),which was attributed to the deposition of particulate aluminum matters with much higher hydration state.Compared with stationary condition,stirring could significantly enhance the deposition process,while the effect of pH on deposition was relatively weak in the near neutral range of 6.7 to 8.7.
Yue ZhangBaoyou ShiYuanyuan ZhaoMingquan YanDarren A.LytleDongsheng Wang
